Html xmls namespace issue URI is not registered (Settings | Languages & Frameworks | Schemas and DTDs)

I have been working on updating a plugin for this issue.  I can successfully put any “xmlns:”   attribute need but the system tells me: "URI is not registered (Settings | Languages & Frameworks | Schemas and DTDs)".  I have tried registeringNamespaces in a class by extending DomFileDescription but it seems the logic for this is only fired off when an XML document is loaded and not an HTML document.

Obviously, the other work around is tell users please go and add these “xmlns URI's” by hand to by going to Settings | Languages & Frameworks | Schemas and DTDs, but it feels like there should be way to register custom “xmlns” namespaces and URI's automatically.  Any ideas?